Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received May 25, 2018; final manuscript received September 21, 2018; published online November 1, 2018. Assoc. Editor: Wenzhong Wang.

Abstract

Friction is usually induced when the contacts are in relative motion, leading to mechanical vibration and consequently heat generation. The reduction of these undesirable parameters is possible by the application of greases, which intends to increase the service life of the bearings. The present work incorporates the frictional and vibration behaviors of concentrated point contact lubricated with bare and nanocomposite greases. The nanocomposite greases were formulated by dispersing different categories of nano-additives like reduced graphene oxide (rGO), calcium carbonate (CaCO3), and alumina (α-Al2O3) in bare grease (BG). The formulated nanocomposite greases are tested for film formation, frictional and vibrational response under a limited supply of greases. The use of transparent glass disk better analyses the profile of film thickness to understand the lubrication mechanism of the point contact. The microstructure of nano-additives and the formulated nanocomposite greases were characterized using high-resolution transmission electron microscopy (HRTEM). The presence of different functional groups in nano-additives and the formulated nanocomposite greases were characterized using Raman spectroscopy. The tribological contact operates under 3% and 30% slide-roll-ratio (SRR) for varying rolling speed (0.001–1 m/s) at a load of 30 N (Hertzian pressure, pH = 0.9 GPa). Film thickness, friction and vibration behavior were recorded to focus the tribo-performance, degree of starvation and dynamics of the tribological contact with slip varying from 3% to 30% SRR. The vibration level was refined to 32% with the addition of rGO nanosheets in BG. The incompatibility of α-Al2O3 with the grease structure results in disruption of tribo-dynamics behavior of the point contact.

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